This invention relates generally to high operating voltage, power, and radio frequency signal amplification, and more particularly the invention relates to a four terminal junction field effect transistor device which exhibits linear rather than square law electrical characteristics with an improved output impedance which allows a higher voltage gain than prior art devices.
High power capability junction field effect transistors have been proposed and patented since the early 1960's. Many of these have followed the Stanislas Teszner design (U.S. Pat. No. 3,274,461) or the Rainer Zuleeg design (U.S. Pat. No. 442,079). These designs have produced products with good performance to frequencies of 500 mega hertz and poor performance (low power gains) up to 1 to 2 giga hertz. The major limitations of the devices are their very low output impedance, low and non linear voltage gains, and a relatively large reverse transadmittance, which reduces the input impedance at high frequencies thereby reducing the achievable power gain at high frequencies (e.g. in the 1 to 5 giga hertz region).
The present invention is directed to modifying a vertical field effect structure to include an additional gate and drain structure which isolates the drain and output electrode from the input gate in a way similar to the action of the screen grid of a tetrode vacuum tube as it acts to isolate the plate signal of a triode from the control grid. The result of adding this additional gate/drain section to the device is a much improved power and voltage gain and a large reduction in reverse transadmittance, which greatly extends the frequency of operation. A second feature is that the linear voltage gain operating characteristic is retained while converting the device characteristics from that of a triode to that of a pentode vacuum tube. The structure of the device is a planar, dielectrically isolated, two lateral section vertical junction field effect transistor. The first section is a vertical JFET with a source gate and drain electrode which is electrically isolated from the second transistor section. The second section comprises a source gate and drain in which the gate and drain are electrically isolated from the first section except the first section drain is connected to the second section source. This results in a four electrode device composed of a source, gate, screen gate and drain, and having the electrical characteristics of a vacuum tube pentode with greatly improved current gain and current handling capabilities as well as improved frequency response.